1. Field of the Invention
The invention relates to a snap ring assembly for carrying punched papers and more particularly to one-piece molded locking hinge binders.
2. Previous Art
A number of binder assemblies have been developed for holding looseleaf papers together. Commonly, these are two, three or more ring looseleaf notebooks and binders utilizing such snap ring assemblies. Binders for English and Metric papers of idfferent sizes, spacings and ring hole counts are common, i.e., English size A and Metric A4 paper. Generally, the snap rings are two or more sets of spaced apart ring pairs that are in substantial registration with each other. The ring pairs can be pivoted from an open condition toward each other and at some predetermined position, are caused to mate together to provide a closed and locked position. The typical binder relies upon a spring-like mechanism to normally urge the ring pairs together in the lock position.
The Papers which are stored in the binder typically include perforated holes along one side that are positioned so that the papers are compatible with and stored by the ring pairs before the ring pairs are pivoted into the closed and locked position. Traditionally, such binder ring pairs have been made from metal. In recent years there has been a move to make such ring pairs from molded plastic polymer.
An example of a typical three ring binder is disclosed in Doffman U.S. Pat. No. 3,995,961. Doffman discloses a binder which includes an integral thermoplastic hollow spline. The spline has three pair of ring halves. One half of each pair is formed as part of movable leaf segments. The leaf segments are integrally connected by scored folding lines to spaced apart walls forming upright edges of the base segment. The folding lines allow pivoting movement for the leaf segments away from and toward the base. The leaf segments are connected to each other by a third folding line. The folding lines allow the leaf segments to move into one of two different rest positions. The first position is with the ring halves open and the third folding line above the upright base edges. The second position is with the ring halves closed and the third folding line below the upright base edges.
One disadvantage with this structure is that it can not be extruded from a mold in the longitudinal direction. Post molding treatment is required due to the presence of projecting ring halves and the closed spine. The mold tooling and process required to accommodate the hollow spline and integral ring halves in a one piece assembly would result in longer cycle times and relatively low productivity.
A disadvantage of the type of structure shown in '961 is that the closure of the rings is secured only by the spring action of the base and upright base sidewalls pressing on the short lever arm formed by the side walls. No positive locking mechanism is provided as part of a one piece assembly in this structure.
Another disadvantage of the hollow spline binders type is that they require more material per unit length than binders of simpler cross-section and thus increase the cost of manufacture.
Another molded binder having side walls and base section with hinged leaf sections is disclosed by Vanni, U.S. Pat. No. 5,018,896. Vanni discloses an elongated base portion extending between separate sidewalls. The sidewalls include respective proximate sections and distal sections having free ends which snap together in the closed position. Closure is maintained by the elastic tension of the sidewalls pressing inward on the distal sections. Vanni teaches that the distal ends of the leaf sections are not integrally connected, but are configured to matingly engage when swung together about the hinge sections. Engagement of the two leaf sections is provided by cooperating male-female configurations such as lip or tongue and groove or channel along the free end of the distal end of the leaf sections. One disadvantage of this method of closure is that it requires additional care by the user in aligning the distal ends of the leaf sections to ensure proper engagement of the opposed tongue and groove configuration.
Vanni also discloses a lock pivotally mounted on one side of a leaf section. The lock is not shown or described but appears to be separate from the end of the assembly. The lock disclosed has a pin which engages a detent on the opposite distal leaf section in a closed position. The detent is a concave depression having a deep re-entrant shape which is difficult to mold with a simple single parting line mold. The locking effectiveness depends on the depth of engagement, and the thickness and strength of material. Under sufficient pull on the rings, the locking arm will flex, the pin will slide and slip out of the detent. There is no positive locking mechanism disclosed which can be molded as part of the one piece assembly.
The closed condition taught by Vanni and Doffman is not provided by a positive locking mechanism but depends on the spring strength of the structure. Thus, a sufficient load of paper or inadvertent shock could cause the rings to spring open with a resulting loss of papers and possible damage.
Both Vanni and Doffman rely on over center motion of the leaf sections and spring action of the flexing outer wall of the sides of the base section. Both disclosures rely on spring action to keep the rings closed.
The design of the assemblies disclosed in Vanni, '896 and Doffman, '961 have re-entrant surfaces which would require other post-molding processes or require molds having slides to accommodate the complex shapes disclosed.
It is desirable to provide a one piece binder that minimizes re-entrant shapes with significant inward angles and does not require post molding treatment or complex molding tooling. It would also be an advantage to provide a binder having a self aligned positive locking member integrally formed as part of the assembly. There is also a need for a more positive locking mechanism not solely dependent on spring force. It is also desirable to provide a binder which provides a simple mechanism for locking and releasing the paper anchoring rings which requires minimal additional manual manipulation.